| The western sub-sag of the Bozhong sag is located in the northwest of the Bozhong Sag in the Bohai Bay Basin.The Paleogene Dongying Formation reservoir is currently an important exploration stratum,and it has undergone complex diagenetic processes during burial,resulting in significant differences in reservoir physical characteristics within different structural zones.However,current research has not systematically explained the reasons for the significant differences in reservoir properties of the Dongying Formation in adjacent areas,and the understanding of the diagenetic response characteristics of the entire western sub-sag region is unclear,This greatly increases the risk and difficulty of exploration.Based on the current research,it is planned to analyze the specific reasons and controlling factors for the significant differences in reservoir physical properties and diagenetic stages of the Dongying Formation in western sub-sag of the Bozhong Sag.This research focus on the clastic rock reservoir of the Paleogene Dongying Formation in the Bozhong Sag.Using scanning electron microscope,thin section identification,fluid inclusion,rock physical property analysis and other technologies to study the petrology characteristics,reservoir pore space and physical property characteristics of the Dongying Formation reservoir in western sub-sag of the Bozhong Sag,divided the sedimentary facies types,classificated the reservoir physical property and evaluated and determined the lower limit of reservoir physical property,The development and distribution characteristics of abnormally high porosity zones have been clarified,and the controlling factors for favorable reservoir development have been identified.The sedimentary facies types in the study area are divided by seismic data and logging data.The sedimentary facies types of the Dongying Formation in the study area are mainly braided river delta,fan delta and sublacustrine fan,of which the first and second members are mainly braided river delta sand bodies,and the third member is mainly fan delta sand bodies.Based on microscopic observation,the reservoir rock types in the area are arkose,lithic arkose.After mechanical compaction,cementation,dissolution and other diagenesis,it is now mainly in the middle diagenetic A1stage and middle diagenetic A2stage,and some well blocks reach the middle diagenetic B stage.The main type of pore development is secondary pores formed by dissolution.The main type of throat is the combination of medium low pore and fine throat.The development depth range of the abnormal high porosity zone in the Dongying Formation reservoir is 2400 m～3400 m.According to the oil and gas evaluation method of clastic rock,the reservoir of Dongying Formation is of medium high porosity and low ultra low permeability.By using static and dynamic methods,the lower limit of porosity and permeability of the Dongying Formation reservoir in the study area was determined to be 15%and 2.1 m D respectively.The reservoir in the study area is affected by sedimentation,diagenesis and other factors.Sedimentation controls the reservoir quality from two aspects of macro facies types and micro sediment structural characteristics,and diagenesis affects the reservoir physical properties from two aspects of constructive diagenesis and destructive diagenesis.The distributary channel microfacies in the braided river delta plain of the Dongying Formation are high-quality reservoirs,and the grain size,sorting,and content of rigid particles are well correlated with the reservoir physical properties;In different structural zones,the burial depth of reservoirs varies greatly,leading to the difference of diagenesis intensity;According to fluid inclusion analysis,oil-water inclusion was formed after strong diagenesis,indicating that oil and gas filling time was late and the improvement of reservoir physical properties was limited. |
